Parse output of witness from ZoKrates CLI stdout and write it to file

[myronrotter]

ZoKrates CLI command zokrates compute-witness writes the witness to file but does not write the output of the witness to file.
However, ZoKrates CLI prints the output of the witness to sdtout. Therefore, as a workaround parse the output of the witness from the ZoKrates stdout and write it to file within the computeWitness function.

Example stdout of zokrates compute-witness:

'Computing witness...\n' +
'def main(_0) -> (1):\n' +
'\t(1 * _0) * (1 * _0) == 1 * _1\n' +
'\t(1 * ~one) * (1 * _1) == 1 * ~out_0\n' +
'\t return ~out_0\n' +
'\n' +
'Witness: \n' +
'\n' +
'["4"]\n'

Output of the witness is: '["4"]'.